NIORAIM Algorithm Applied to a Multiconstellation GNSS: Analysis of Integrity Monitoring Performances in Various Phases of Flight

P. Madonna, S. Viola, L. Sfarzo

Abstract:	Many studies have been conducted on RAIM to use GNSS navigation systems in those fields where very strict performances are required. In safety-of-life applications, such as aviation, in critical phases of flight such as approach and landing, integrity plays an extremely important role and integrity monitoring functions become necessary. To perform such task many algorithms have been proposed: NIORAIM is one of the most promising. NIORAIM uses non-uniform weights applied to the pseudo-range measurements of satellites involved in the position solution lowering the integrity levels, thus improving integrity availability at the cost of a very slight degradation of accuracy of the position solution. A paper previously presented by the authors at the ENC-GNSS 2009 Conference, showed a particular method used to determine “ad hoc” weights. Such method computes the values of the integrity levels following a worst-case philosophy for integrity monitoring. Each value corresponds to the largest of the integrity limits computed using a mathematical technique which uses a numerical integration of the bivariate Gaussian density function so that the probability within the missed detection region is exactly equal to the specified allowable rate. Matlab® simulations showed a remarkable improvement of integrity availability reached with NIORAIM compared to another RAIM algorithm in the NPA, APV-I and APV-II phases of flight. Afterwards the NIORAIM FDE algorithm was implemented in a real GNSS monitoring system actually used to monitor GPS+SBAS service for ATC applications. Due to the algorithm computational burden and given the strict processing constraints of such ATC system, a further innovative approach was developed to obtain an operable NIORAIM algorithm. The implementation of NIORAIM algorithm in the real GNSS monitoring system showed the remarkable improvement of integrity availability achieved with respect to another legacy RAIM algorithm, so confirming the theoretical expectations. The performances achieved by the implemented Fault Detection section of the NIORAIM algorithm were tested under bias conditions, in a single fault hypothesis, so characterizing its sensitivity and the results were published at the IAIN World Congress 2009. In this paper the NIORAIM algorithm is extended to a multiple satellite constellations: GPS+GLONASS. As the environment in which the algorithm operates is changed, it needs to be adapted to reflect the new scenarios. Modifications to the NIORAIM algorithm previously implemented are necessary and the problem of handling two simultaneous satellite faults is taken into account. This paper describes the theoretical approach used and the RAIM availability performed, in the APV-I and APV-II phases of flight, through the application of the NIORAIM algorithm with the increase number of ranging in view, GPS+GLONASS. The paper also discusses the fault detection capability in presence of dual-fault situations. The simulation results show that the application of the NIORAIM algorithm to a multiconstellation improves the integrity availability with respect to that achieved by the algorithm in case of single satellite constellation. Studies are underway aiming to develop a real-time NIORAIM algorithm using the multiconstellation in a GNSS monitoring system in order to develop a product which can be used for aviation applications.
Published in:	Proceedings of IEEE/ION PLANS 2010 May 4 - 6, 2010 Renaissance Esmeralda Resort & Spa Indian Wells, CA
Pages:	1258 - 1263
Cite this article:	Madonna, P., Viola, S., Sfarzo, L., "NIORAIM Algorithm Applied to a Multiconstellation GNSS: Analysis of Integrity Monitoring Performances in Various Phases of Flight," Proceedings of IEEE/ION PLANS 2010, Indian Wells, CA, May 2010, pp. 1258-1263. https://doi.org/10.1109/PLANS.2010.5507342
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